Sugarcane beetles causing problems for Alabama corn growers

• Since they’re feeding directly below the soil surface, it makes them difficult to get at.
• If you get a lot of damage from sugarcane beetles, the only solution may be to plow it all up and start over.

In evaluating the insect pests of corn in Alabama, one that has been numerous in recent years and might be numerous again this year is the sugarcane beetle, says Kathy Flanders, Auburn University Extension entomologist.

“Sugarcane beetles are attracted to light, so you’d think that they’d be out there and you could find them,” said Flanders at the recent Central Alabama Corn Production Meeting in Autaugaville.

“But they don’t really like sunlight, so you have only a short amount of time to catch them on top of the soil.”

Seed treatments and more traditional at-planting insecticides like Lorsban and Counter have proven effective, she says. “In Mississippi, they’re finding that a half-rate of those products plus a seed treatment can give you the protection you need from this pest.”

The beetles are about one half-inch to five eighths-inch long, says Flanders.

“They love to feed at the bottom of the corn plant, right where the growing point is when the plant is young. So they’re coming out just when the plant is coming in, and they love to get in and feed. They feed from the outside, gouging large holes through the side of the base of the corn.”

Since they’re feeding directly below the soil surface, it makes them difficult to get at, she says.

“The net result is that when the plant begins to grow out, you get these dead heart symptoms. So when the corn tries to re-grow, the plants won’t amount to anything. If you get a lot of damage from these, the only solution may be to plow it all up and start over.”

Some growers, says Flanders, are more susceptible to sugarcane beetle than others. “The No. 1 thing is if you try and plant corn into pasture or hay fields, directly into the grass sod. They like to hang out in that grass sod. The next one will be corn with a lot of pasture around it. And sometimes, fields just seem to get sugarcane beetle, depending on the environment around the field.”

Reduced-tillage fields also have shown more susceptibility to sugarcane beetles.

Low pH can lead to problems

“Fields with low pH also seem to be more susceptible to having problems with sugarcane beetles,” she says. “Bahiagrass also may attract these insect pests. I saw some bahiagrass pastures in South Carolina this year damaged by the sugarcane beetle. We don’t normally think of it as doing so much damage in bahiagrass, but that’s what was happening in these fields. They were drought stressed and had low pH.”

Small fields surrounded by woods also seem to get hit by the sugarcane beetle, along with fields that are near lights, she adds.

Adult sugarcane beetles over-winter, come out and feed on the corn plants, and then they go out and lay eggs in permanent sod, explains Flanders.

“The larvae don’t do very well when the eggs are laid in corn. Sugarcane beetle grubs feed during the summertime, eating organic matter. The adults come out in the spring and in the fall, and you may see them flying around. They go back into the soil to spend the winter, and then they’ll come out in the spring, looking for food to eat before they start laying eggs.

“By the time you find out you’ve got these pests, it’s pretty much too late to try and put out any rescue treatments. So you need to pick your seed treatment. If you know you’ll be planting corn in one of these high-risk situations, especially like corn after pastures, you need to be finding a hybrid that is sold with a high rate of seed treatment.”

Growers should remember, says Flanders, that all seed treatments are not created equal.

“Most seed treatments do a good job on specific insects. If you’re in a high-risk situation, I’d recommend you find a hybrid with the 500-rate of Poncho, because that would offer you some protection. A rate of 1250 would be even better. Of course, the higher rate of insecticide, the higher the cost of the seed, but it can be well worth it to protect your stand.”

But just because corn is planted after pasture doesn’t mean you’ll get sugarcane beetle every year, she says.

“I don’t know when this epidemic of sugarcane beetle will go away. But in the last few years, each year has been a little bit higher than the previous year. We saw scattered instances throughout the state, so it doesn’t seem to be one specific soil type. It also gets into sweet potatoes and causes problems.”

Fields that are at risk for sugarcane beetle should be scouted frequently (at least twice weekly) from crop emergence until the plants are 8 to 12 inches tall. If sugarcane beetles and/or damaged plants are found, a foliar spray with Lorsban or one of the registered pyrethroids may kill the adult beetles before they cause further damage. Do not replant corn into an infested area while adult beetles are still present.